I used to able UF goal 3.5 litter per session no problem

For context I'm on hemodialysis for 2 years now and still on IJC (if it somehow could be relatable to my question please simply ask for detail on why) when I first started hemodialysis, I couldn't achieve that UF goal because simply lack on information like you need to eat and knows your dry weight so and so on so complications of hemodialysis wont happen but recently (past 9 session, I couldn't finished 2.5 liter UF goal without cramping especially if move on the chair a lot. Sorry for broken English, English is not my first language. Any1 know why?